Single-hung and double-hung windows are the most prevalent types of windows in North America. They have a sought-after traditional appearance and operate by sliding upper and lower window sashes up and down within a window frame. Two main advantages of double-hung windows are their easiness of operation and their traditional style.
While they offer a pleasing traditional aesthetic look, double-hung windows have two main disadvantages: they are not as airtight as other windows and they have limited ventilation. Insulating strips, also called weather strips in double-hung windows are usually located within the lateral sides of the frame of the sashes or in lateral channels of the outer window frame. In other types of windows having better insulating properties, such as casement windows, the weather strips are usually placed between the window frame and the sash frames such that when wind blows upon the window, the weather strips are compressed between the sash frames and the window frame, providing better insulation.
Now with regard to ventilation, double-hung windows work by sliding the top sash down or the bottom sash up. This means that only half of the window remains open at one time. Some types of awning windows offer the look of double-hung window by having an upper panel fixed above a mullion and a lower panel which can be pivoted horizontally about its lower rail, within the lower portion of the window frame. However, such type of window also requires that one of the sashes stays closed while the other one is open. In addition, the degree of aperture of the pivoting window is limited. Such windows also often require cranks and complex hinge assemblies to maintain the window opened. The evermore stringent requirements for windows with better insulating properties have forced windows manufacturers to offer double and even triple thermal insulation windows. In other words, each window sash or window panel includes two or three glass panels retained within the frame of a sash. The weight of each window sash is thus considerably increased. Stronger and more complex counter-weight devices must be used with these types of thermally insulated window panels, especially with double-hung windows, in order to remain easy to open.
There is a need for a window assembly having the pleasing traditional aesthetic look of a double-hung window while offering better insulating properties, and increased ventilation. There is also a need for a window assembly which can accommodate two or three glass panels per window frame, while remaining easy to open, without requiring expensive or complex balance devices. Of course, it would be desirable for this window assembly to present an aesthetic, lean and simple design from inside as well as from outside the building.